add interactives/embeddable-production.html

there is now a 'default' environment that is used for the interactives.html
and embeddable.html. This way a server like lab.staging.concord.org
can have its default be staging so a user doesn't need repeat the word
staging.
download lab files from lab.tar.gz

the create-archived-public-dir script will now use site-version by
default. And it will also look up the default URL that is used by
the embeddable.html page.
[#68604690]